The present invention relates to a chuck jaw apparatus and more specifically to a quick change mechanism for a top jaw assembly having replaceable pads.
A conventional chuck jaw includes a master jaw mounted on a chuck body, and a top jaw mounted on top of the master jaw. The top jaw is typically provided with a gripping surface adapted to engage a work piece and hold it during machining operations. Normally the gripping surface of the top jaws are machined after they are mounted on the master jaw to assure concentricity of all the gripping surfaces with respect to the axis of the chuck. Each time the top jaw is replaced, the new jaw must be bored after it is mounted. The lost time incurred during the remounting and reboring of the top jaws during changeovers or setups means that productivity of the machine is reduced.
In order to reduce the downtime during changeovers and setups, it is known to use a replaceable work holding pad which is clamped to the top jaw using a quick change clamping mechanism. During changeovers and setups, only the work holding pads need to be replaced. While these types of chuck jaws reduce downtime, they have several drawbacks.
First, most master jaw mounting surfaces are not in the same axial plane. For this reason, most top jaws are machined prior to mounting so that the user can qualify support surfaces. However, the pad axial location is usually established prior to machining the top jaw. Thus, no matter how accurately the top jaws are manufactured, some axial alignment is lost during assembly of the top jaw onto the master jaw.
Another drawback associated with these types of chuck jaws is that the clamping mechanism used for securing the pad to the top jaw tends to push the pad away from its support surface increasing misalignment. If the pads are not seated properly against their support surfaces, the work piece gripping surfaces will not be concentric with the axis of the chuck.
Still another problem with prior art chuck jaw assemblies is that the clamping mechanisms employed to secure the work holding pads to the top jaw are relatively complicated. This results in increased costs in manufacturing and assembling the chuck jaws.